1. Field of the Invention
The present application relates to a passive component, and more particularly to an over-current protection device.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Thermistors are used to protect circuits to avoid over-temperature or over-current damages. A thermistor typically includes two electrodes and a resistive material between them. This resistive material has low resistance at room temperature, and the resistance will abruptly increase to a thousand times when the temperature reaches a threshold temperature or over-current occurs in the circuits, so as to suppress over-current for circuit protection.
When the temperature decreases to room temperature or over-current no longer exists, the thermistor returns to low resistance. Then the circuit operates normally. In view of the advantage of recovery, thermistors can replace fuses to be widely used in high density circuits.
The trip of the thermistor mainly depends on the composition thereof. In consideration of the need of low working temperature for batteries, low-temperature materials having low trip temperatures are often used. As a result, the hold current of the themistor is decreased. For battery applications, thermistors with high hold currents at high temperatures, e.g., 60° C. or 70° C., and rapid trip below 80° C. are required. However, it is difficult to obtain such thermistors by merely modifying the composition therein. High hold currents can be achieved by using high-temperature material such as high density polyethylene (HDPE), but the high-temperature material cannot meet the requirement of rapid trip below 80° C. If low-temperature material such as low density polyethylene (LDPE) is used, rapid trip below 80° C. can be achieved; however, high hold current at 60-70° C. is not obtainable. Therefore, it is difficult to achieve not only high hold current but also low-temperature trip for over-current protection.